The use of composite structures in the aerospace industry has become more and more prevalent due to the desirable properties of composites, especially low weight, high strength and stiffness, resistance to corrosion, and damping characteristics among other properties. Composite materials are now being used for aircraft wings, horizontal and vertical stabilizers, nose and tail cones, and other aircraft structural elements. The advantageous properties of composites have increased aircraft performance benefits, including increased range, decreased fuel consumption, and greater payload. Added performance benefits guide the use of composites throughout the aerospace industry. However, the primary shortcoming of composites has been high cost, and the aerospace industry is continuing to explore ways to improve the cost of composite manufacturing while maintaining the performance benefits of composite materials. In particular, potting compound structural reinforcement used in the assembly of composite structures is one area that includes additional cost due to waste.
Composite structures typically include honeycomb cell cores or other structurally enhanced cores. Potting compounds, typically epoxy based syntactic foam in the aerospace industry, are inserted into selected sections of the cores to add structural integrity for specific applications to the panel. Many potting compounds that are used for this purpose are “single part,” that is they are pre-mixed and applied in one step. Single part potting compounds are high viscosity putty-like compounds that are susceptible to forming pockets of air contamination from handling and processing.
Generally, potting compounds such as these have been inserted into composite cell structures through a vacuum bag technique. In these techniques, the composite panel is masked to expose cells for inserting potting compound. Then patties of potting compounds are stacked over the composite panel and a vacuum bag is placed over the panel and patties. A vacuum is drawn and the bag then pressures the compound into the cells. The vacuum also assists to remove displaced air pockets within the cells. Due to the high viscosity of the potting compounds, however, pockets of air sometimes remain trapped within the cells or between patties. If post production analysis of the composite reveals undesirable air contamination, then the panel will require rework and reapplication of the potting compound to ensure that air pockets are not present. Therefore, it would be advantageous to reduce the susceptibility of air contamination while inserting potting compounds.
Once the insertion of the potting compound into the cells is complete, the excess potting compound is waste. In fact, the vacuum bag technique generally creates waste of one and a half to twice as much potting compound as is inserted into the cells. The excess potting compound is required in order to avoid under fill and voids in individual cells. Unfortunately, the excess potting compound is now deformed and may have inadvertent pockets of air contamination that proscribes its reuse in other filling operations. The excess is discarded and this results in a cost of one and a half to twice as much expense on potting compound for the amount used. Therefore, it would be advantageous to reduce the cost of inserting potting compounds by reducing the amount of waste generated.
It should also be noted that the excess potting compound removal techniques are manual and quite labor intensive. Generally, the excess must be scraped off by hand with a trowel. Again, this contributes to the cost of production. Therefore, it would be advantageous to reduce the labor cost of removing the excess potting compound.